1. Field of the Invention
This invention relates to the extraction and collection of one or more analytes by a sorption process. Specifically, this invention relates to a device and method for performing direct vial extraction.
2. Description of the Related Art
To prepare samples for chemical analysis, often analytes, or the compound of interest, must be separated from a sample matrix, such as water, soil or animal tissue and presented in a form suitable for a particular piece of analytical equipment, such as a gas or liquid chromatograph. There are various extraction methods known and used to collect and prepare samples for such chemical analysis. These methods include liquid/liquid extraction, solid phase extraction, solid phase microextraction and stir-bar sorptive extraction. The trend in the industry is toward simplified sample preparation that results in pollution prevention and waste minimization.
Liquid/liquid extraction partitions an analyte between two immiscible phases, such as an organic solvent and an aqueous phase. When an aqueous phase contains the analyte it is extracted into the immiscible organic solvent by placing the two phases into contact. Extraction is enhanced by mixing. A relatively large volume of solvent (typically greater than 100 mL) is necessary to carry out the extraction. Partitioning of a compound between the solution solvent and extractant solvent is governed by the distribution constant, K, and the phase ratio, r (The ratio of the quantity of the solvent to that of the other phase). An example of such an extraction would be EPA test method SW846 3510 which specifies that one liter of aqueous sample should be serially extracted with 350 mL of methylene chloride. When the entire procedure is considered, a total of 500 mL of solvent is used for each sample. The solvent extract must be evaporated to reduce its volume to between 1 and 2 mL for placement into an autosampler vial prior to analysis.
Solid phase extraction (SPE) is often used to extract a sample prior to analysis by chromatography. SPE uses silica particles with an organic layer covalently attached to the surface of the particles. The silica particles are packed into a tube or disc, such as a polyethylene syringe barrel. The sample is then prepared and an analyte extracted by passing the sample through the solid sorbent. The analyte is then desorbed from the SPE media by solvent extraction. An example of such an extraction is EPA test method SW846 3535 which utilizes one liter of sample but requires approximately 50 mL of solvents. The solvent extract must be evaporated to reduce its volume to between 1 and 2 mL for placement into an autosampler vial prior to analysis.
It is known in the art to use a sorbent to extract an analyte from a solution. The analyte is later extracted from the sorbent by thermal desorption or by back extracting with a small amount of organic solvent. Sorption materials are usually homogenous, non-porous materials that are above their glass transition point (Tg) and in which the analyte can dissolve. The sample may be removed for analysis by thermal desorption or solvent extraction.
Solid phase microextraction (SPME) is an extraction technique wherein a fiber is coated with a sorbent layer. The coating may be a polysiloxane or other immobilized sorbent. The fiber is immersed in a liquid or exposed to its headspace during which time the analyte is retained. The fiber may then be inserted into a gas chromatograph injection port for analysis where it is thermally desorbed or may be back extracted with a suitable solvent. SPME is not accepted for EPA test methods.
Stir-bar sorptive extraction (SBSE) is used primarily for direct mode sampling. SBSE utilizes a thick sorbent coating on a magnetic bar stirrer that stirs the sample for a predetermined amount of time during which time the analyte partitions between the stir-bar sorbent and the sample. After extraction, the stir-bar is removed and the analyte is thermally desorbed to the injection port of a gas chromatograph.
Examples of the prior art follow:
U.S. Pat. No. 5,595,653 issued to Good et al. on Jan. 21, 1997 discloses an apparatus for extracting an analyte from a liquid sample. The apparatus comprises a microcolumn having a microparticulate media sandwiched between two compression layers. The compression layers are preferably a binder-free glass fiber, held in the microcolumn by upper and lower polypropylene mesh.
U.S. Pat. No. 5,635,060 issued to Hagen et al. on Jun. 3, 1997 discloses a solid phase extraction or chromatographic medium. The medium comprises a porous nonwoven fibrous matrix comprising at least one of polytetrafluoroethylene and blown microfibers, and sorptive or reactive hydrophobic siliceous molecular sieve particulates enmeshed in the matrix.
U.S. Pat. No. 5,911,883 issued to Anderson on Jun. 15, 1999 discloses a solid phase extraction article having a porous, particle loaded, fibrous sheet material spiral-wrapped around its axis is provided. The sheet material is wound around itself to provide multiple layers of sheet material, each layer of sheet material being spaced from each adjacent layer of sheet material.
U.S. Pat. No. 5,897,779 issued to Wisted et al. on Apr. 27, 1999 discloses a cartridge device for removing an analyte from a fluid. The cartridge comprises a hollow core, a sheet composite comprising a particulate-loaded porous membrane and, optionally, at least one reinforcing spacer sheet. The particulate is capable of binding the analyte and the sheet composite is formed into a spiral configuration about the core.
U.S. Pat. Nos. 5,415,779 and 5,595,649 both issued to Markell et al. on May 16, 1995 and Jan. 21, 1997, respectively, disclose a particle loaded, porous, fibrous compressed or fused article for separations and purifications. The article comprises a nonwoven fibrous polymeric web, which preferably is thermoplastic, melt-extrudable, and pressure-fusible blown microfibrous web, and sorptive particles enmeshed in the web.
U.S. Pat. No. 5,472,600 issued to Ellefson et al. on Dec. 5, 1995 discloses a gradient density filter made from sheets of blown polypropylene microfibers where the microfibers of at least one of the sheets have an effective fiber diameter less than that of the other sheets.
U.S. Pat. No. 5,403,489 issued to Hagen et al. on Apr. 4, 1995 discloses a method and apparatus for performing solid phase extraction (SPE) on a fluid that contains solubles and suspended solids. The apparatus includes a conduit, a SPE medium located in the conduit, and a fluid flow direction altering mechanism or a SPE rotating mechanism.
U.S. Pat. No. 5,391,298 issued to Pieper et al. on Feb. 21, 1995 discloses an apparatus that can be used to perform a solid phase extraction under pressurized conditions. The apparatus includes a pressurizable housing with an inlet tube that can communicate with a pump, which feeds a liquid to the housing under positive pressure. A disk assembly includes fluid-permeable, porous sheets on opposite sides of an SPE membrane.
U.S. Pat. No. 5,279,742 issued to Markel et al. on Jan. 18, 1994, reissued as U.S. Pat. No. Re. 36,811 on Aug. 8, 2000 discloses a method for isolating an environmentally hazardous organic contaminant from a fluid utilizing a solid phase extraction medium. The medium comprises a PTFE fibril matrix, and sorptive particles enmeshed in the matrix. The separations can be efficiently performed in a stacked disk format.
U.S. Pat. No. 5,691,206, issued to Pawliszyn on Nov. 25, 1997 discloses a device for carrying out solid phase microextraction. The device is a fiber, solid or hollow, contained in a syringe. The syringe has a barrel, a plunger slidable within the barrel and a hollow needle extending from the end of the barrel opposite the plunger. The needle contains the fiber. When the plunger is depressed, the fiber extends beyond a free end of the needle and when the plunger is in a withdrawn position the fiber is located within the needle. To collect a sample, the needle is inserted through a septum in a bottle containing the sample and the fiber is extended into the sample. After a predetermined amount of time, the fiber is returned to the needle and the syringe is withdrawn from the bottle. The sample is analyzed by inserting the needle through a septum in a gas injection port of a gas chromatograph and extending the fiber.
U.S. Pat. No. 5,565,622, issued to Murphy on Oct. 15, 1996 discloses a simplified method for solid phase extraction of components of interest from a sample. A syringe is used in which the inner surface of the cannula or needle is at least partially coated with a stationary phase such that aspirating the sample into the needle results in adsorption of the components of interest into the stationary phase. Aspiration of a solvent may be employed for removing the components of interest from the stationary phase for direct injection into a chromatographic instrument, or the components of interest may be removed by thermal desorption, wherein the needle is placed in the injection port of the chromatographic instrument and heated.
U.S. Pat. Application Pub. No. US 2002/0105923, applied for by Malik, published on Oct. 17, 2002 discloses a method of preconcentrating trace analytes by extracting polar and non-polar analytes through a sol-gel coating. The sol-gel coating is either disposed on the inner surface of the capillary tube or disposed within the tube as a monolithic bed.
It would be an improvement to the art to have a device in which the extraction may be performed and the analyte conveniently and transportably stored for later analysis.